There is an item that can increase your actual card storage in shop, also theres a lot of amount that you can get from there and it costs you 150 Jewels for most of them

Also for Collection page, you have to spend 400 jewels for it every time when you are going to open one

*You can also get few of card storage item for increasing the amount from Holy Token summons in Step 2 or 3 if i'm not wrong-

No, it can be used anytime whenever you bought one (meaning as long as the item is in inventory, and when its activated, it should be a permanent increase on card storage/deck cost etc.)

Idk exactly the limit of collection pages, but afaik its probably around 60 if im not wrong